A climatological study of tropical thunderstorm clouds and lightning frequencies on the French Guyana Coast

Abstract

The climatological conditions that are favorable to thunderstorm cloud development in the coastal zone of French Guyana are investigated. The analysis reveals that both the thunderstorm occurrence and the mean monthly lightning frequency are correlated to the Intertropical Convergence Zone annual oscillation, thus increasing from March to August when the South‐East trade‐wind flux drives continental air masses towards French Guyana and decreasing from September to February when French Guyana is under the influence of maritime air masses driven by the North‐East trade‐wind. The study of the lightning frequency values, observed during individual thunderstorm events, as a function of the cloud‐top height shows that these values are intermediate to the lightning frequency values deduced from the parameterizations proposed by Price and Rind (1992) for typical continental and maritime thunderstorm clouds of a similar height. This behavior suggests that the air masses in which thunderstorm clouds develop in the French Guyana coast are mixed air masses with intermediate characteristics. Further, the absence of correlation between the lightning frequency values and both the cloud‐top heights and the corresponding convective available potential energy (CAPE) values indicates that these parameters can not be used to predict lightning activity in these clouds. Most probably, the aerosol concentrations in the subcloud layer and consequently the cloud droplet concentrations play an important role in the development of lightning activity in the considered clouds.

Smoking Rain Clouds over the Amazon

“…Here, we see that, although the radiative effects of the smoke suppress the BL clouds, the microphysical effects overpower this radiative suppression and produce clouds that are more violent than can be found in microphysically maritime environments. These observations support suggestions (9,29) that aerosols play a major role in the determination of the dynamic, microphysical, and cloud electrification properties that distinguish continental from maritime convection (30).…”

Flood or Drought: How Do Aerosols Affect Precipitation?

“…from shallow clouds (17,20,21,(26)(27)(28) and invigorate deep convective rain clouds with warm (>~15°C) cloud base (29)(30)(31)(32)(33), although the impact on the overall rainfall amount is not easily detectable (34,35). These observations are supported by a large number of cloud-resolving model studies (36)(37)(38)(39)(40)(41)(42)(43).…”

“…Even if the total rainfall amount is not decreased by the increase in aerosols, delaying the formation of rain is sufficient to cause invigoration of cloud dynamics. By not raining early, the condensed water can form ice precipitation particles that release the latent heat of freezing aloft (6,29,30) and reabsorb heat at lower levels where they melt after falling.…”

Contribution to the climatological study of lightning

“…It is usually expressed in terms of lightning frequency F which is a function of the thunderstorm cloud electrification degree and is related to the dynamical and microphysical cloud characteristics, i.e. cloud top height H, maximum vertical velocity w, convective available potential energy CAPE, droplet concentration N (Price and Rind, 1992; Rutledge et al, 1992; Molini6 and Pontikis, 1995;. The study of the climatological evolution of the global lightning frequencies by using a GCM implies the use of F parameterizations depending upon model predictable parameters.…”